Application No. 992 9791.3, filed in the United Kingdom on Dec. 16, 1999, and from which the present application claims priority under 35 U.S.C. xc2xa7 119, is hereby incorporated by reference.
1. Field of the Invention
The invention relates to a method of monitoring interference currents, particularly, but not exclusively, in railway trackside signaling systems.
2. Description of Related Art
The introduction of power electronics in the traction systems of railway vehicles which is generally desirable has increased the possibility of interference with trackside signaling, communications and power supply systems. It is possible for harmonics to be generated in the earth return current from the traction system that are of sufficient magnitude and duration at specific frequencies to cause the track circuit relay to respond. Under certain conditions this can lead to a momentary signal change from red to green. This clearly has great safety implications.
Industry standard GS/ES1914 provides details relating to the permissible interference levels in trackside signaling equipment. By way of example, the standard provides that the interference levels should be set at less than 48 mA for Reed track circuits. This provides a target of about 5.3 mA for the measurement of interference currents in the presence of traction currents, which may be on the order of several kA.
It is known to measure the interference currents induced in trackside signaling using a combination of transducers to record the traction current and frequency. The transducers are typically installed on a test train which must be run up and down the track which is under study. The data recorded is then extracted and analyzed.
This procedure is time consuming, taking typically one or two days, and can result in too much analysis being undertaken and can also seriously extend the re-testing requirements. All of this is clearly undesirable. Accordingly, a method for carrying out the interference current monitoring and analysis more rapidly is needed.
In accordance with exemplary embodiments of the invention, interference currents in railway trackside signaling apparatus are monitored by first and second transducers adapted to measure the traction current and frequency, respectively. An instantaneous interference current value is determined, based on data output from the first transducer. Data output from the second transducer is used to determine digital filter outputs for the trackside signaling frequencies for the interference current value. The determined interference current value and digital filter output values are recorded on a data storage medium and displayed on a display unit.
The invention provides advantages over prior art methods in that it permits the data to be displayed on a real time basis. This in turn leads to much faster analysis of where, and under what conditions, false signals can be induced in signaling equipment.
In an exemplary embodiment of the invention, for a predetermined frequency corresponding to a frequency used in a trackside signaling system, the instantaneous interference current value is compared with a predetermined value. If the current value exceeds a first predetermined limit, a warning signal is displayed on the display unit. If the current value exceeds a second predetermined limit, a danger signal is displayed on the display unit.
In accordance with an exemplary embodiment of the invention, the warning and danger signals are displayed as bar graphs. A point signal is also displayed. In the event of a warning and danger signal being displayed on the bar graph, the point signal can be switched to reflect the warning or danger signal.
In accordance with an exemplary embodiment of the invention, the instantaneous interference current value is compared with a predetermined value for each frequency used in a trackside signaling system.
In accordance with an exemplary embodiment of the invention, a data recording device is adapted to record data relating to vehicle speed and vehicle transmission settings.
In accordance with an exemplary embodiment of the invention, a data recording system is provided for recording data output from the first and second sensors, and includes a clock adapted to record the instantaneous time at which each current value is recorded.